Conventionally employed as an etching method is a plasma etching for etching an object to be etched by using a plasma. Employed in such a plasma etching method is, for example, an etching apparatus including a lower electrode and an upper electrode disposed opposite to face each other within a hermetically sealed processing vessel. In the etching apparatus, an object to be etched having a mask formed on a surface thereof is mounted on the lower electrode and a processing gas is supplied into the processing vessel. Thereafter, a high frequency power is applied to the lower electrode to excite the plasma, thereby executing the plasma etching.
The plasma etching method is widely employed to form a predetermined pattern on a surface of an object to be etched such as a semiconductor wafer and a liquid crystal substrate. The pattern thus formed has a size of the order of micron, in general.
Recent diversification in technical field will make it almost surely a necessity to form a recess with an opening dimension of the order of millimeter in the course of, for instance, microfabricating a jig for the formation of an integrated circuit.
FIG. 9 provides a schematic cross sectional view of an object to be processed 10 having a recess with an opening dimension of the order of millimeter which is formed by the conventional etching method. The object to be processed 10 shown in FIG. 9 is obtained by way of etching a semiconductor wafer 12 to be etched in accordance with the conventional etching method by using a desired pattern previously formed on a photoresist 14 provided on the semiconductor wafer 12 as a mask. A recess 20 thus formed in the wafer 12 is of a substantially cylindrical shape and its opening dimension (diameter) R ranges, for example, from 10 to 30 mm.
When the recess 20 with the opening dimension of the order of millimeter is formed by the conventional etching method as described above, a peripheral portion 24 of a bottom surface of the recess 20 may happen to be etched deeper than a central portion 22 thereof (hereinafter referred to as a “subtrench shape”). However, in most applications, it is preferable that the bottom surface of the recess is flat. In fact, the subtrench shape of the recess impedes a precision fabrication of various devices.